The present invention relates to a crash protection structural component which is capable to take up energy primarily in a non-reversible manner in response to a compression load applied in the longitudinal axial direction of the crash protection component.
Crash protection components are, for example, needed in the construction of motor vehicles for taking up energy in case of an accidental crash. On the other hand, these components shall also be capable of taking up energy in a reversible manner when the load is relatively small. When the load increases, the energy take-up must be irreversible, at least in such a manner that the energy is not released directly after it has been applied to the protection component.
Such structural components are used, for example, for supporting the front and rear bumper relative to the supporting chassis of the vehicle or relative to the forward ends of the longitudinal carrier beams. Such carrier beams are generally part of the vehicle structure. In case of a crash impact such longitudinal carrier beams must take up a large proportion of the crash energy.
Such energy take-up is determined by the size of the integral EQU .intg.F.multidot.ds
wherein F is the force applied by the crash and s is the displacement. This integral defines the surface area in a force displacement diagram of such a structural component which is enclosed between the displacement axis, for example, the abscissa, and the force curve. FIG. 1 shows an idealistic force curve as a function of the displacement. This surface area, especially the section thereof representing a high plastic, irreversible, take-up of energy shall be as large as possible. Stated differently, the force shall remain constant as the displacement increases.
Structural components for the purpose of taking up energy in an irreversible manner have been constructed heretofore on the basis of two long established principles. One principle involves hydraulic damping, whereby kinetic impact energy is first converted into friction which in turn is converted to heat, whereby liquids or small spheres are employed, see for example French Patent No. 617,230 or German Patent No. 468,279. The other principle involves the deformation of a metallic material beyond its proportionality limit. The proportionality limit defines the point where the deformation becomes plastic and irreversible as a result of the energy take-up. Such structures are, for example, formed as corrugated tubing or as a carrier beam section in the form of a sheet metal part which starts folding in response to a predetermined compression load.
All prior art structures of this type are subject to substantial disadvantages. One undesirable feature is the relatively large weight of these crash protection components of the prior art, whereby the weight of a vehicle is necessarily increased to an extent that its fuel consumption is also increased and that an increased wear and tear is imposed on road surfaces.
Another disadvantage is seen in the rather costly manufacturing and in the fact that prior art crash protection devices are trouble prone. For example, hydraulic dampers have many trouble-prone elements such as pistons, cylinders, guides, valves, seals and so forth. Failure of any one of these components may reduce or eliminate the effectiveness of the hydraulic damper for its intended purpose.
Structural damping components of metallic materials, particularly steel sheet metal, such as corrugated pipes or folding sheet metals must be manufactured by complicated deep drawing or other deformation processes. Such processes are generally rather energy consuming and involve high temperatures and high pressures for softening or deforming of the material. Another source of failure of this prior type of structure is the corroding of the steel sheet metal.